Conductive materials have been developed by the assignee of the present invention for various applications such as the screening of such materials as powders, inks or pastes onto substrates and subsequent fusing under controlled conditions to form electrically conductive paths.
Of the conductive metals, copper is one of the more attractive because it has better conductivity than gold but is considerably cheaper. One of the major problems encountered in the fabrication of conductive lines on substrates using copper powder or an alloy powder consisting of a copper powder and other alloy metal powders, or viscous ink or paste containing the copper powder, is that commercially available copper powders have varying degrees of surface oxides which adversely effects the conductivity of the copper conductors. In fact, the copper oxide layer on the surface has a melting temperature as much as 157.degree. C. higher than the pure metal, in accordance with the Cu-O phase diagram. Disadvantageously, this oxide layer must be broken down before complete fusing or melting can occur and therefore less control over the final quality of the melted conductive material and possible loss of electrical conductivity in the conductors can result. To my knowledge, there is no system of which I am aware for removing metal oxides from metal powders used in the manufacture of electrical conductor inks or powders.
It is accordingly one object of the present invention to remove oxides from metal powders to enable the powders to be applied wet or dry, quickly heated and fused to a substrate.
Another object is to remove metal oxides from copper powders to lower the temperature at which the powders will fuse together and bond to a substrate.
Yet another object is to obtain more precise control over the melting point of the powder material.